The broad goal of our research is to reach a better understanding and control of intracellular protein degradation. Arginase in rat liver is a particularly good model because the degradation rate can be varied over a wide range depending on the enzymes which initiate the degradation of arginase. In vitro studies of the inactivation of arginase by an ATP-stimulated protease isolated from liver and other proteolytic enzymes are underway. We are also studying the association-dissociation and unfolding equilibria of arginase and the effect of Mn plus 2 and substrates on these equilibria, in an effort to see if these factors are important in the degradation of arginase.